John S Lewis

Saturday, August 27, 2016

The steady improvement of techniques for detecting
extrasolar planets has borne fruit—and a low-hanging fruit at that.The nearest star to the Solar System, Proxima
Centauri, has been found to have a planet (imaginatively named Proxima Centauri
B) with roughly Earth-like size and even Earth-like temperatures.This is fascinating news, but what does it
really mean?Is this really another
Earth?

The press has been all over this story, and some of
what has been written makes sense.But
what reliable knowledge do we have?

First, this is indeed a rocky terrestrial-type
planet.It is the closest known planet
to the Solar System, and indeed orbits the star that is the Sun’s nearest
neighbor.Interstellar distances, even
for nearest neighbors, are huge: Proxima Centauri (let’s call it Proxy) is 4.24
light years away from us, a dizzying 270,000 Astronomical Units (1 AU is the
mean distance of Earth from the Sun).That’s 64,000 times as far as Jupiter is at its closest to Earth.

The mass of the planet is estimated to be 1.3 times
the mass of Earth.Its radius and
density are unknown.It orbits once
every 11.2 Earth days at an average distance of 0.05 AU from Proxy, following a
path whose eccentricity is so far unknown.Proxy is a faint red Main Sequence star, of spectral class M6, with a
mass of about 0.123 times the mass of our Sun and a luminosity only 0.17% of
the Sun’s—but almost all of that light (about 86% of it) is infrared (heat) radiation
invisible to the human eye.It is a
member of the family of flare stars, undependable neighbors that emit powerful
and unpredictable flares. The star’s photosphere (its visible surface) is at a
mere 3000 Kelvins, cool enough for “clouds” of refractory metals and oxides to
form.

It is likely that Proxy orbits around the common
center of mass of the Alpha Centauri (α Cen) system, but far enough from α Cen
that its orbital period must be on the order of a million years.

A planet forced to live in such close proximity to
its star suffers a variety of indignities.The first is that the erratic activity of the star subjects the planet
to extreme brightness fluctuations and to bombardment with high fluxes of
X-radiation near times of maximum activity.The second is that tidal friction can quickly despin the planet, causing a
rotational lock between the star and planet.Third, if the planet is too close to its star, the planet may cross
the Roche limit and be torn apart by the star’s tidal forces.Proxy B certainly suffers from the first of
these afflictions and certainly does not suffer from the third: if it were
inside the Roche limit there would be no planet to detect, only a debris disk;
a super asteroid belt.The intermediate
fate, falling into a rotational lock, is unavoidable in such close quarters,
but there are several distinct outcomes with very different significance, and
for which we presently lack the data to choose between them.

The simplest possibility, if the orbit of Proxy B is
nearly circular, is for it to simply lock directly onto Proxy and always keep
the same face toward its star.With the
Sun shining on only one side of the planet, the sub-solar point would be quite
hot, and half of the planet would be frozen in eternal night.Volatile gases would migrate into the
darkness and freeze out on the surface, making vast deposits of water ice,
carbon dioxide ice, and other gases, and perhaps generating lakes of liquid argon
and the heavier inert gases krypton and xenon.Nitrogen and oxygen, if present, would fall as snow on the night
side.Any slight eccentricity of the
planet’s orbit would cause it to rock back and forth once per year (in the case
of Proxy B, one year is just 11.2 Earth days). The strong solar tidal forces on
the planet would cause the rocking to damp out and the orbit to become more
perfectly circular.This is called a 1:1
spin-orbit resonance, like the Moon around Earth or many satellites of the
outer planets around their primaries.

But we have no guarantee that the planet’s orbit is
closely circular.A sobering example is
provided by Mercury, a tidally despun planet locked onto its star (the Sun) but
with a significant orbital eccentricity.It actually rotates in a 3:2 spin-orbit resonance: three planetary
rotations in two planet years.At
consecutive perihelion passages, opposite points on Mercury’s equator face the
Sun.Thus two regions get alternately
scorched—and frozen.Because of the
gravitational stresses, the planet ends up slightly elongated with two bumps on
opposite sides of the planet’s equator.At perihelion passage the angular rate of rotation of Mercury and its
angular rate of motion along its orbit are almost exactly equal, so that the
“hot pole” tracks the Sun rather closely for many days near perihelion.Other resonant relationships besides
Mercury’s 3:2 resonance are also possible, but they have the potential for
disaster: 2:1 and 5:2 and 3:1 resonances are associated with such large orbital
eccentricities that they raise the potential for collision with other
planets.Note that 2:1 and 3:1
resonances would have the same spot on the equator being baked on each
perihelion passage; 3:2 and 5:2 resonances would have the strongest heating
localized alternately in two regions on opposite sides of the planetary
equator.

We don’t yet know the orbit of Proxy B well enough
to distinguish between these different states.But we can see that some of these states would generate extreme temperature
and weather behavior that would not be conducive to maintaining a biosphere—and
that’s without even considering the effects of wild luminosity and flare
activity by the star.

Oh, and one other thing: Proxy B is so close to its
star that it is quite near the point at which the tidal forces of its star
would disassemble the planet and turn it into an asteroid belt.Bummer.

But if the planet is in, say, a 3:2 resonance--and all its volatiles don’t go gentle into that good night—the
star will remain on the Main Sequence, providing heat to its planets, for
another 4000 billion years.No need to rage against the dying of the
light.

Saturday, April 23, 2016

About three years ago,
shortly after the launch of the Chinese Shenzhou
9 spacecraft in 2012 with female “Taikonaut” Liu Yang aboard, I was
interviewed on television by a woman reporter who seemed quite impressed by the
fact that China had a real female astronaut.She was aware that the first female space traveler was Valentina Tereshkova,
who flew a mission in the Soviet Union’s Vostok
program ‘way back in 1963, and wondered why the United States didn’t have
female astronauts.

I was confounded by the
question: it was like being asked why gravity had stopped working, or whether I
had stopped beating my wife!Perhaps a
little summary is in order here.

The first woman to
travel in space was indeed Valentina Tereshkova.I actually would hesitate to call her an
astronaut; “state-sponsored space tourist” would be a better description.Her employment as a textile worker seemed
poor preparation for piloting a spacecraft: she was not trained as a pilot,
engineer, or scientist. According to my
Russian friends, she was trained in space flight to the extent of being “warned
not to touch anything”, which I view as a probable overstatement by jealous
men.However, she had a background as a parachutist,
an important factor. The rationale for
flying a parachutist was explained as giving her the option of jumping out of
the Vostok capsule “if something went
wrong”.(In reality, it was always far safer to jump out than to
remain aboard, because the spherical Vostok
capsule and its Voskhod successor had
the nasty habit of rolling downhill upon touchdown, much to the detriment of their
occupants.)

The argument that Tereshkova
was pioneering the way for Soviet women astronauts is ludicrous: the next
Soviet woman cosmonaut was not to fly for another 19 years!That woman, Svetlana Savitskaya, flew on the Soyuz T-5 mission to the Salyut 7 space station in July, 1982.She was a real astronaut, well trained and
competent to do far more than touch the controls.Two years later she flew a second time, on
the Soyuz T-12 mission, becoming the
first woman to fly in space twice and also the first woman to go on a
spacewalk.

In 1978 NASA had
selected a new class of astronauts, including several women.It was clear that by 1983 NASA would begin
launching female astronauts into orbit.It is reasonable to interpret Savitskaya’s flight as being a preemptive
strike, timed to beat NASA’s women astronauts into space-- but she was a real
astronaut!

The first American
woman to fly in space, Sally Ride, a Ph. D. physicist from Stanford, flew two
Space Shuttle missions (STS 7 and STS 41G, in 1983 and 1984 respectively).
She was followed in quick succession by
Judith Resnik (STS 41D and STS 51L in 1984 and 1986) and Kathryn
Sullivan (three flights, STS 41G, STS 31, and STS 45 in 1984, 1990, and 1992, plus one spacewalk).Anna Fisher flew on STS 51A in 1984, and Margaret Seddon flew three STS missions
between 1985 and 1993.

Shannon Lucid flew five separate space missions between
1985 and 1996, the last being a visit to the Mir space station.She also
has the unusual distinction that she was the first woman born in China to fly
in space.

Bonnie Dunbar followed
with five Space Shuttle missions from 1985 to 1998, and a number of other
American female astronauts have flown three, four, or five missions since that
time.

As of April 2016, the
totals look like this:

·Forty-four American women have flown in
space, for a total of 116 missions.

·Two Canadian women (Roberta Bondar, on STS 42; Julie Payette on STS 96 and STS 127) have flown a total of three Space Shuttle missions,

·Two women from Japan (Chiaki Mukai on STS 65 and STS 95; Naoko Yamazaki, STS
131) have also flown a total of three missions.

·Two Chinese women (Liu Yang, Shenzhou 9; Wang Yaping, Shenzhou 10) have each flown one
mission. (The political significance of the launch of China’s first female
space traveler can be judged by the fact that it occurred precisely on the 49th
anniversary of the launch of Valentina Tereshkova.)

Thursday, April 21, 2016

Those of you who do not read the Journal
of Geography and Natural Disasters before breakfast each morning missed
something interesting.On 17 March that
journal published a paper by M. J. Kelly of Cambridge University on the subject
of “Trends in Extreme Weather Events since 1900- An Enduring Conundrum for Wise
Policy Advice”.Now, we know that human
activities have added a lot of carbon dioxide to the atmosphere since 1900, and
we know that CO2 has a net warming effect on the planet.Numerous press reports have claimed that global
warming must cause an increase in the frequency and severity of extreme weather
events.Interestingly, the
Intergovernmental Panel on Climate Change (usually familiarly referred to as
the IPCC), which has consistently warned about anthropogenic global warming
(AGW), has never endorsed this position.

Global warming, according to both model calculations
and observations, causes the most warming at higher latitudes and the least
warming near the equator.In the
language of meteorology, the meridional
temperature gradient (the temperature contrast between equator and poles)
is decreased.But global weather is
driven primarily by that gradient: when the meridional temperature gradient is
large, polar air is colder relative to equatorial air, so the pole-to-equator
density contrast of Earth-surface air is larger, exerting larger forces to drive
dense polar air toward the equator and vice
versa.The cold air sinks and flows
equator-ward, the warm air rises and flows pole-ward, and the Coriolis effect
diverts these flows into giant circulation patterns, including (at the extreme)
cyclones and hurricanes.A larger
temperature contrast between equator and poles causes larger density differences and pumps more energy
into these global-scale motions.More
energy in the same mass of air means higher velocities.In other words, the obvious effect of global
warming is to reduce the temperature contrast and cause lower wind speeds.

And of course, we humans injected vastly less CO2
into the atmosphere in the 50 years from 1900 to 1950 than we did in the
following 50 years: therefore AGW must have been much stronger in more recent
history.

But so much for how things “ought” to work: Dr.
Kelly has (gasp!) actually looked at the data on weather extremes to address
this issue.He found that “the weather
in the first half of the 20th century was, if anything, more extreme
than in the second half”.In other
words, the actual quantitative data on weather extremes confirms the
common-sense understanding of a decreased meridional temperature gradient and
agrees with the consensus of the IPCC, but flatly contradicts the glib
prophecies of impending doom of the fear-mongers.These prophecies, though quantitatively
unfounded, have the PR virtue of being frighteningly draconic and easily
understood by politicians and policy makers who think and argue qualitatively. But who gets more attention, the person who says "Tomorrow will be a little better than today", or the one who shouts "Disaster coming!"?

Dr. Kelly concludes, “The lack of
public, political and policymaker appreciation of the disconnect between
empirical data and theoretical constructs is profoundly worrying, especially in
terms of policy advice being given.”

You don’t have to take my word for
this.The original technical publication
is available online:

Tuesday, April 19, 2016

A recent article on space.com (http://www.space.com/30236-jupiter-great-red-spot-color-secrets.html?cmpid=NL_SP_weekly_2015-08-14)
tells of the efforts of a team of NASA scientists at Goddard Space Flight
Center to replicate the striking brick-red color of Jupiter’s famous and
long-lived Great Red Spot (GRS). Most
of Jupiter is covered by alternating bands of bright clouds (zones) and dark
clouds (belts), in which the GRS is embedded: however, the red color of the GRS
appears to be distinctly different from the brown belts, suggesting two or more
different coloring agents.

Carl Sagan and his colleagues
long argued for organic matter as the coloring agent; this suggestion, however,
depends on the achingly slow destruction of methane by ultraviolet sunlight,
which makes largely uncolored products at such a slow rate that the atmosphere
would have to remain stable and unmixed for millions of years to accumulate a
detectable tinge of brown.Carl gave
these largely imaginary organic coloring agents the name “tholins”, a name that
has stuck with us while the organic coloring agents that supposedly justified
the name have largely disappeared from the Jovian literature as being
quantitatively indefensible: another clear example of the victory of the charmingly
qualitative over the less-romantic quantitative.

The Goddard team wisely concentrates on the predicted
ammonium hydrosulfide (NH4SH) cloud layer (misidentified in the
article as ammonium sulfide, (NH4)2S), the level that we
see when we peer into Jupiter’s belts, the next cloud layer below the white
ammonia-crystal clouds that cover most of the planet, especially the bright
zones.They presumably chose that layer because
fresh ammonium hydrosulfide, a colorless crystalline substance, is very
sensitive to ultraviolet light and rapidly turns brown when exposed to
sunlight. Space.com explains, “Studies
predict that Jupiter's upper atmosphere is composed of clouds of ammonia,
ammonium hydrosulfide and water”.I’m
rather partial to these cloud layers because I am the author of the generally
accepted cloud models of Jupiter and its fellow giant planets [J.S. Lewis, The Clouds of Jupiter and the NH3-H2O
and NH3-H2S Systems. Icarus10, 365 (1969)].Yes, that’s 1969.

The
space.com article explains that the Goddard team is “baking some of the
components of Jupiter's atmosphere with radiation, mimicking cosmic rays”. They also report that their simulation “heats
up hydrogen sulfide and ammonia” to make ammonium hydrosulfide, a remarkable
assertion that makes no sense.Actually,
the way to make ammonium hydrosulfide, both on Jupiter and in the lab, is to cool down a mixture containing ammonia
and hydrogen sulfide gases to precipitate a “snow” of the solid.As for the “baking”, the temperature of that
cloud layer is both predicted and measured to be about 225 K (-48 oC;
-54 oF), a pretty bracing temperature for baking!

OK, now they have solid NH4SH.What next?They blast the solids with high-energy particles, “much as cosmic rays
blast Jupiter's clouds”.Now, they have
good reason to expect color changes because the much less violent and simple
exposure of this cloud-stuff to sunlight has the same effect.

But wait a minute!Doesn’t the Sun also shine on Jupiter?How important are cosmic rays compared to the
ultraviolet part of sunlight?Good
question!The cosmic rays hitting
Jupiter carry about 0.001 ergs of energy per square centimeter per second (of
which only a tiny proportion actually goes to make colored products).The energy supplied by the part of
ultraviolet sunlight energetic enough to make colored sulfur compounds out of H2S
(all the sunlight with wavelength less than 270 nanometers) is nearly 1000 ergs
per square centimeter per second.In
other words, whatever the importance of cosmic rays, sunlight is about a
million times more important!

So hydrogen sulfide makes Jupiter-colored
products.How could we have missed this,
back in that earlier millennium?Well,
we didn’t.Ron Prinn and I pointed this
out long ago: J.S. Lewis and R.G. Prinn, Jupiter's Clouds: Structure and
Composition. Science169, 472 (1970).In that article, we showed that the rate of
solar UV destruction of hydrogen sulfide (and production of yellow-, orange-,
and brown-colored sulfur compounds) should surpass the total rate of methane
photolysis claimed by Sagan and coworkers by a factor of 100,000.This would occur only in those regions of
Jupiter where the topmost (crystalline ammonia) cloud layer was thin or absent;
i. e., in the belts but not in the zones.The belts remain white because the ammonia-snow clouds block sunlight
from reaching the deeper levels where the sulfur compounds reside.

But this explanation did not apply to the Great Red
Spot, which is, after all, red.Prinn
and I addressed this issue a few years later, after
phosphine gas (PH3) was detected on Jupiter (R.G. Prinn and J.S. Lewis, Phosphine on Jupiter and
Implications for the Great Red Spot. Science190, 274 (1975)).Our argument was straightforward: that the
dynamically active GRS was the best place on Jupiter for accumulation of red
phosphorus made by solar UV destruction of phosphine: strong vertical winds
blow phosphine gas up to altitudes above the protective ammonia clouds, where
it encounters UV light and makes red phosphorus; the vertical winds then help
levitate the particles of red phosphorus up where we can see them.This process would occur at a rate governed by
the relatively large proportion of UV radiation that is energetically capable
of destroying PH3 and NH3 compared to that capable of
destroying methane: red phosphorus would be produced at a rate hundreds of
times faster than the total rate of destruction of methane (the ultimate source
of all organic matter, both colored and uncolored), and thousands of times faster
than the rate of formation of colored organic products.

Where do
cosmic rays figure in this argument?They don’t.The total energy flow
from cosmic rays is about a million times smaller than the rate of production
of colored sulfur compounds.Even if the
cosmic rays produced colored products with 100% efficiency, which they don’t, their
effects would remain negligible.

Then there is that spectacular
image of “cosmic rays blast(ing) Jupiter's clouds”. “Blasting” at one millionth of the intensity of ultraviolet sunlight”?Really?Sounds more like an advertising slogan to me.

Since 2005 I
have had the pleasure of being an expert commentator on China Central
Television (CCTV) for “civil” space missions, including both the manned flight
program (Shenzhou and Tiangong) and their series of Chang-e lunar probes.After a three-year lull in Chinese manned
spaceflight activity, that program is set to resume this fall.

Since the
3-person Shenzhou 7 mission in 2008,
Chinese manned spaceflight has centered on the Tiangong 1 space station module.This module, announced on CCTV in 2008, and originally slated for flight
in 2010, was launched into orbit on 29 September 2011 on a Long March 2F booster.(The
delay in launch date was further extended by a safety review occasioned by the
launch failure of a Long March 2C
booster in August.)The module, similar
in size and weight to a Shenzhou
spacecraft, although very different in design, weighs in at about 8.5 metric
tonnes.

The first
visit to TG1 was by an unmanned spacecraft (Shenzhou
8) launched on 17 November 2011, a precursor mission to test all systems
before human occupation of the module. The spacecraft remained attached for 12 days
before SZ8 was recalled to Earth.Several
months later, on 16 June 2012, three Chinese astronauts (“Taikonauts”),
including one woman, Liu Yang, were launched into orbit on Shenzhou 9.The flight
featured two docking events with TG1, one computer-controlled and one manually-directed,
with return to Earth after 11 days.The Shenzhou 10 mission, also with a crew of
two men and one woman, Wang Yaping, flew a year later, launching on 11 June
2013.After a 15-day flight, featuring
several undocking and docking tests with Tiangong
1, SZ10 was successfully returned to Earth.

It was
originally planned that the Tiangong 1
module would be de-orbited in 2013; however, it still remains in space in April
2016, but is apparently no longer crew-rated.To replace it, the Tiangong 2
module is scheduled for launch in the third quarter of 2016.It is apparently a slightly modified version
of Tiangong 1.

Manned
missions to Tiangong 2 are planned to
begin in October or November of 2016, ending a 41-month hiatus.

More
ambitious human space endeavors await the debut of the Long March 5 booster.The
launch facilities for LM5 on Hainan Island have been completed and on-pad tests
of an LM5 rocket (not necessarily a flight article) have commenced.The first launch of the LM5, long planned for
mid-2015, can be expected before the end of the year.LM5, comparable to the Russian Proton or American Saturn I boosters, will carry payloads of up to 25 tonnes to Low
Earth Orbit, permitting direct launch of a large second-generation space
station module in the 2020 time frame. LM5 will also have a trans-lunar
injection capability of about 8 tonnes, allowing a manned lunar flyby or
orbital mission with a crew of two or three, followed by return to Earth.It is likely that such a mission would be
preceded by Earth reentry tests of unmanned Shenzhou
capsules at lunar-return velocities (11 km/s).The energy dissipated during a return from the Moon is twice that of the
same vehicle returning from LEO, so two-step reentry profiles such as
skip-glide trajectories may be expected.The development of these capabilities will mirror the Soviet Zond probe development program using the
Proton booster: Kosmos 146 and 154 tests
in March and April of 1967 of lunar manned-mission hardware, the Zond 4 launch into high Earth orbit in
March 1968, the Zond 5 launch in
September 1968, a “cabin” carrying a dummy cosmonaut for an unmanned flyby of
the Moon and return to Earth, and Zond 6
in November 1968 for a similar lunar flyby mission and recovery.By the usual conservative standards of the
Soviet space program, three consecutive successful unmanned tests would be
required before launching a cosmonaut on the same mission profile.The launch pad turnaround of two months meant
that the next (and final) unmanned precursor would probably be expected in
January.But the American Apollo program was ahead of schedule,
and in December 1968 the Apollo 8
mission was dispatched on a lunar-orbiting mission: 48 tonnes, three
astronauts, and days in lunar orbit.Zond 7 was not yet ready to fly its
mission: one cosmonaut at best (and probably none), 6.6 tonnes, on a lunar
flyby without orbiting the Moon; embarrassingly non-competitive.In the heat of the space race, Zond 7 was simply put on indefinite
hold.

Zond 7 was finally launched in August 1969 as
a repeat of the same unmanned mission profile, a month after the American Apollo 11 mission landed Neil Armstrong
and Buzz Aldrin on the Moon; too little and too late.

Upcoming Shenzhou missions to Tiangong 2, beginning with Shenzhou 11 this November, will practice
rendezvous and docking activities, develop experience with longer mission
durations, and prepare the way for Moon-oriented manned missions in the Long March 5 era.Operating without the frenzied intensity of
the Space Race, China can progress deliberately and cautiously, minimizing
uncertainties and risks, on its own schedule—and using 21st century
technology.Watch for the emergence of a
Chinese manned lunar flyby (or orbiter) mission once LM5 is operational, well
before manned lunar landing hardware has been developed.And watch for unmanned precursors, especially
high-speed reentry tests!

Thursday, March 31, 2016

Last summer, on 30 July
2015, a spectacular airburst occurred over northern Iran, in the mountains west
of Tehran.The site of the reported fall
is near the town of Avaj, in Qazvin County.Press reports mention shattered windows and light structural damage to
buildings.

There are reports of
recovered meteorites, complete with plausible, if not wholly convincing,
pictures.I even received an email from
someone in Iran offering to sell me a stone from the fall, accompanied by a
putative analysis that claims 20% carbon and doesn’t mention silicon.At least, that what the message appears to mean: it bears all the
earmarks of a machine translation from low Martian.So what hard facts do we have to work
with?Virtually none.

Perhaps the most
notable fallout from this event has been the fuss kicked up on the
internet.There has been the most
astonishing display of ignorance, prejudice, millennialist vitriol, and
bigotry, liberally salted with insane conspiracy theories.I have seen the following charges: 1) it’s a
lie by the Iranian government, 2) a cover-up by NASA, 3) a harbinger of the end
of the world, 4) a divine portent of unknown significance sent by Allah, 5)
evidence of the God of Israel’s intent to destroy Iran, 6) a stray Russian
missile, 7) an Israeli missile, 8) a baseless rumor denied by the Iranian
government, etc.A number of comments
appear to have no content, simply serving as vehicles for incoherent rantings,
misspellings, tortured grammar, and severe mental confusion from which no
meaning can be extracted.It’s a paranoid
madhouse.I have read close to 50 such comments,
of which two show evidence of both knowledge and sanity.

So, dear reader, here
is my summary: we don’t know diddly-squat about this particular event.Statistically, however, airbursts are not
rare and reports of minor damage have many historical precedents.As for using this natural event as an omen,
well, any idiot can make up some such nonsense.There is overwhelming evidence that they can—and do—exactly that.Many such predictions of the end of the world
have been issued, none of which have come true.For your amusement, readhttps://en.wikipedia.org/.../List_of_dates_predicted_for_apocalyptic_events.

The question of why something happens is enormously
interesting, but these examples of “man’s search for meaning” show our pathetic
incompetence in this task.It is
wonderful to contemplate why
something happened, but any explanation beyond physical causality is often
simply baseless speculation, rarely testable by observation, and, when tested,
almost invariably found to be wrong.We
would be far better engaged in studying the how,
what,when and where of events,
where physical evidence can be brought to bear. But speculation about
underlying causes is fun!

Test yourself: The
(true) given fact is, “The first German artillery shell fired on Leningrad in
World War II landed in the zoo and killed the only elephant in Russia.”

The press is full of
the news that a new Earthlike planet, Kepler 452b, has been discovered by the
revived Kepler planet-hunting
spacecraft.The discovery of a planet
“much like Earth” garners more attention because the planet orbits in the
so-called “Goldilocks zone” around its star, the range of distances within
which water can exist as a liquid on its surface rather than only as ice or hot
vapor.

Kepler 452b is 60%
larger in diameter than Earth and is presumed to have Earthlike composition,
although it is important to note that there is as yet no way of measuring its
mass.Nonetheless, the phrase “Earthlike
world” has the press reeling, including suggestions that worlds like this are
the places radio astronomers should look to find radio signals from intelligent
aliens.

OK, let’s play this
game and see what Earthlike composition would imply.A diameter of 1.6 times Earth’s means a
surface area of 1.6x1.6, or 2.56 times Earth’s, and a volume of 1.6x2.56, or
4.1 times Earth’s.Assuming Earthlike
material, this planet would have a core/mantle/crust structure very similar to
Earth’s, but the internal pressures would of course be significantly higher,
and the core and mantle material must be compressed to higher density than
Earth’s average of 5.5 grams per cubic centimeter, probably close to 7.5 for
the whole planet.Now, that would
generate a planet with 5.6 times Earth’s mass.This mass and diameter would correspond to a surface gravity that is
5.6/2.56 times Earth, 2.18 times as large, or 21.4 meters/second2.

“Similar composition”
means similar abundances of radioactive elements, which decay inside the planet
and eventually lose their heat by radiating heat from the planetary surface
into space.This planet, generating 5.6
times as much heat as Earth, which it radiates into space through a surface
with area 2.56 times Earth’s, so the heat flux (Watts per square meter per
second) is about 2.2 times Earth’s.At
steady state, with heat loss rate equal to heat production rate, this requires
that the temperature gradient in the crust (the rate at which temperature
increases with depth) must be 2.2 times as large as on Earth.

Mountains can build up
only to a finite height because the temperature gradient under them leads to
softening and melting of the continental rock deep under them.On Earth the Himalayas rise about 13
kilometers above the abyssal plains of the oceans.Mars has half the radius of Earth, so its
heat flow and temperature gradient should be about half that of Earth, meaning
that softening of the rock should occur about twice as deep, and Martian
mountains should build to about twice the height as on Earth.In fact, the highest peak on Mars, Olympus
Mons, rises about 26 km above the plains.Of course, to calculate this precisely we need to account for the
slightly lower density of Mars and its slightly lower surface temperature, but
we still get a similar answer.

Now let’s apply that to
Kepler 452b.The topography, Earth’s
standard scaled down by a factor of 2.2, would have the highest mountain regions
about 6 kilometers above the abyssal plains.Now let’s think about the oceans on this world.On Earth, there is enough water to make a
layer about 4 km deep covering the entire planet.Kepler 452b, if it has the same composition
as Earth, would contain 5.6 times as much water spread out over a surface area
that is 2.56 times as large.Thus it
would contain enough water to make a layer 2.56 times as deep as Earth’s 4 km,
or about 10.2 km deep.Since the highest
land would rise about 6 km from the abyssal plains, this means that the tops of
the highest mountains would lie roughly 4 km below mean sea level.Thus
Kepler 452b, if truly Earthlike in composition, would be a true water world.

Now consider the
conditions on the sea floor.An ocean
10.2 km deep in a gravity field of 2.2 Earth gravities would exert tremendous
pressure at the ocean floor: the weight of the ocean exerts an average pressure
of 2240 atmospheres, which is essentially the highest pressure at which pure
liquid water can exist, irrespective of temperature.At approximately this pressure, water freezes
to make dense (sinking) ice III rather than familiar (floating) ice I.Such an ocean could start to freeze from the
bottom up.

We’re also told the planet
has had liquid water for 6 billion years or more, without mentioning how the
luminosity of its parent star (and the surface temperature of the planet) have
changed over time.

Of course, with data on
the mass of the planet we could see whether it really is a “terrestrial” planet
or a sort of warmed-up ice ball: if the latter is the case, then the planet
could be much less dense and the ocean much deeper.

So this is “Earth
2.0”?

If you are interested
in the wonderful game of designing planets that accord with the laws of
physics, astronomy, and chemistry, you can find a number of examples in my 1998
book Worlds without End, which
explores the possibilities for many types of planets allowed by nature, but not
present in our Solar System.

John S. Lewis

John S. Lewis is a professor emeritus of planetary science at the University of Arizona’s Lunar and Planetary Laboratory and is Chief Scientist at Deep Space Industries. His interests in the chemistry and formation of the solar system and the economic development of space have made him a leading proponent of turning potentially hazardous near-Earth objects into lucrative space resources. Prior to joining the University of Arizona, Lewis taught space sciences and cosmochemistry at the Massachusetts Institute of Technology. He received his education at Princeton University, Dartmouth College and the University of California, San Diego, where he studied under Nobel Laureate Harold Urey. An expert on the composition and chemistry of asteroids and comets, Lewis has written such popular science books as "Mining the Sky", "Rain of Iron and Ice", and "Worlds without End".